Thermal energy storage (TES) systems using phase change material (PCM) have been recognized as one of the most advanced energy technologies in enhancing the energy efficiency and sustainability of buildings. Now the research focus is on suitable methods to incorporate PCMs within buildings or the materials used to construct the buildings. There are several methods to use phase change materials (PCMs) in thermal energy storage (TES) for different applications. Microencapsulation is one of the well-known and advanced technologies for better utilization of PCMs with building parts, such as walls, roofing material, and floors, besides within the building materials themselves. Microencapsulated phase change materials as latent heat thermal storage (LHTS) systems for building applications offer a challenging option to be employed as an effective thermal energy storage and retrieval device.
One type of PCM is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed or released when the material changes from solid to liquid and vice versa; thus, PCMs are classified as latent heat storage units.
Also, PCMs as latent heat storage units have been used in textiles, packaging, electronics, etc. For example, the PCM may be encapsulated and included in a winter jacket as a microcapsule. The microcapsule, specifically the PCM, would initially absorb the wearer's body heat and store it (via melting of the PCM) until the body temperature drops from the outside temperature, at which time the heat stored in the PCM is released (via solidification of the PCM), thereby giving warmth to the wearer. Throughout the process, the capsule wall contains the PCM.
Micro- or macro-encapsulation involves some disadvantages such as super cooling, and instability of some hydrates. The encapsulation process can also raise the cost of thermal energy products substantially in comparison to bulk PCMs. Also, capsules can be susceptible to rupture and/or leakage of the PCMs. Since the development of microencapsulated PCMs, there has been a constant need for improved storage vehicles for phase change materials, in particular one that does not include microencapsulation.
Form stable compositions based on phase change materials and porous structured materials have been reported by Zhang D. Tians, Xiao D. Development of thermal energy storage concrete, Cement Concrete Res 2004; 34(6): 927-34. The porous structured material may be expanded perlite as taught by CN 101121876 and by A. Sari and A. Karaipekli, Preparation, thermal properties and thermal reliability of capric acid/expanded perlite composition for thermal energy storage, Material Chemistry and Physics 109(2008) 459-464. The limitations to these current disclosures for impregnating expanded perlite with a PCM is that vacuum impregnation is required along with pretreatment of the perlite to remove bound water therefrom. Additionally, the amount of the PCM introduced into the expanded perlite is only sufficient to yield a material with a ΔHf of 90 J/g.
There is a need for a more efficient and cost effective continuous process of impregnating an absorbent material such as expanded perlite with a PCM, in particular one that does not require the use of vacuum and one that can hold more PCM in the same size particles, and hence yield higher enthalpy values.